The shifts of stretching vibration frequency of the radicals in salicylic acid and the interaction of entrainer and solute in supercritical CO2 with the addition of entrainer by using infrared spectroscopy were studied. The stretching vibration frequency of both radicals C=Oand O—Hshifted towards a lower frequency with ethanol as entrainer
while the stretching vibration frequency of radical C=Oshifted towards a higher frequency with acetone as entrainer. The results showed that the solubility of salicylic acid in supercritical CO2 with ethanol as entrainer was much higher than that with acetone as entrainer. The influence of the action of hydrogen bond was much stronger than the action of solvent polarity on the increase of solute solubility.